Memory devices are typically provided as internal, semiconductor, integrated circuit devices in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Changes in threshold voltage (Vt) of the memory cells, through programming (which is often referred to as writing) of charge storage structures (e.g., floating gates or charge traps) or other physical phenomena (e.g., phase change or polarization), determine the data state (e.g., data value) of each memory cell. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, cellular telephones, solid state drives and removable memory modules, and the uses are growing.
Memory cells may be configured to operate as what are known in the art as single-level memory cells (SLC) or multi-level memory cells (MLC). SLC and MLC memory cells assign a data state (e.g., representing a respective value of one or more bits) to a specific range of threshold voltages (Vt) stored on the memory cells. Single level memory cells permit the storage of a single binary digit (e.g., bit) of data on each memory cell. Meanwhile, MLC technology permits the storage of more than one binary digit per memory cell (e.g., two bits, three bits, four bits, etc.), depending on the quantity of threshold voltage ranges assigned to the memory cell and the stability of the assigned threshold voltage ranges during the lifetime operation of the memory cell. By way of example, one bit (e.g., 1 or 0) may be represented by two threshold voltage ranges, two bits by four ranges, three bits by eight ranges, etc. Non-binary numbers of threshold voltage ranges are also known, e.g., using two memory cells configured to operate with three data states to collectively store three bits of information, or 1.5 bits per memory cell. As a single memory cell is used to store higher levels of data, differentiating data states can become more difficult.
Programming in memories is typically accomplished by applying a plurality of programming pulses, separated by verify pulses, to program each memory cell of a selected group of memory cells to a respective intended data state (which may be an interim or final data state). With such a scheme, the programming pulses are applied to access lines, such as those typically referred to as word lines, for selected memory cells. After each programming pulse, one or more verify pulses are used to verify the programming of the selected memory cells. Current programming typically uses many programming pulses in an incremental step pulse programming scheme, where each programming pulse is a single pulse that moves the memory cell threshold voltage by some amount. Programming operations are generally power intensive operations of a memory device.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative methods of programming memory, and apparatus to perform such methods.